1. Field of the Invention
The invention relates to an adjustable-length gas spring comprising a housing having a central longitudinal axis, a piston rod led out of the housing concentrically of the central longitudinal axis, a piston arranged on the piston rod and displaceable in the housing and dividing the housing into two partial housing chambers, and a valve for the partial housing chambers to be connected with each other.
2. Background Art
In an adjustable-length gas spring of the generic type known from EP 0 564 776 A1, the adjusting arrangement is a hydraulic adjusting arrangement, the triggering device of which is provided with elastic locking tongues which are lockably engageable with the gas spring. Locking projections of the locking tongues engage with a rear recess allocated to the gas spring. This solution is satisfying as far as the locking engagement is concerned, but the manufacturing requirements are comparatively complicated. In addition, the hydaulic adjusting arrangement is hard to operate.
A gas spring with an adjusting arrangement is known from DE 42 36 732 A1, in which the cable of a Bowden cable is stationarily fixed to the gas spring and the hose surrounding the cable bears against an operating pin.
A gas spring with an adjusting arrangement comprising a Bowden wire is known from DE 41 14 101 A1. To this end, an operating lever is articulated to the end of the piston rod, actuating a valve pin that is disposed in the hollow piston rod.
An adjustable-length gas spring is known from U.S. Pat. No. 4,793,450, in which a valve between two partial housing chambers can be opened or closed by means of a fluidic triggering device to be actuated by an actuating bellows.
The drawback of all the known designs resides in that extraordinarily high operating forces are needed to open the valve.